This invention relates to satellites and roll/yaw controls therefor, and particularly to a roll/yaw control of a satellite equipped with pitch momentum bias and moving in a polar or near-polar orbit with the aid of a magnet coil interacting with the earth's magnetic field.
Known attitude control systems, such as described by K. T. Alfriend and R. E. Lindberg in Geomagnetic Field Effects on the Design of a Magnetic Attitude Control System, Nordwjk, October 1977, control the roll/yaw attitude by using an earth sensor for roll angle measurement, using a magnetometer for measuring the pitch and roll components of the earth's magnetic field, and by using a magnet coil, in the pitch axis, as a correcting element. In the latter system, the velocity of variation of the pitch component of the geomagnetic field is used to control the nutational motion, while the roll component of the geomagnetic field is used to change the direction of the spin vector. A disadvantage of such systems resides in the fact that they require magnetometers and a filter for suppressing the earth's rotational frequency in the magnetometer signal. Moreover, special precautions must be taken to avoid influencing the magnetometers with the field of the magnet coils.
An object of the invention is to improve satellites and roll/yaw controls therefor.
Another object of the invention is to avoid the aforementioned disadvantages.
Yet another object of the invention is to provide a control system which is free of these disadvantages, but without magnetometers.